Specialized coatings are often used with electronic devices, especially microelectronic devices. Such coatings are used to provide shielding or blocking functions with respect to potentially harmful energy or electromagnetic radiation, for example. Such shielding can be used to protect a device from external energy sources and/or help contain energy emitted by an internal source. Thus, these coatings are often referred to as radio-opaque. Coatings can also be used to protect against tampering or reverse engineering. In this regard, these coatings are usually designed to cover all or some portion of an electronic device. Moreover, these coatings are usually designed to conform to weight and size restrictions and to minimize the number and complexity of steps to form the coating.
Various techniques can be used to provide coatings on electronic devices, one of which is known as thermal spraying. Examples of thermal spraying or coating processes include arc spraying, flame spraying, and plasma spraying. Thermal spraying generally refers to any process where metallic and/or non-metallic materials are deposited, in a molten or semi-molten condition, on a surface to form a coating of the material with a desired thickness. In this process, a thermal spraying nozzle provides a heated zone. The material to be deposited, in a powder or finely divided form, is passed through the heated zone of the spray nozzle under the force of a flowing gas or the like. As the materials are heated, they change to a plastic or molten state and are accelerated by the flowing gas. The particles are then directed to the surface to be coated. The particles strike the surface where they flatten and form thin platelets that conform and adhere to the irregularities of the surface and to each other. As the sprayed particles impinge upon the surface they coalesce, cool, build-up, and form a coating. Exemplary thermal spraying systems and processes for coating electronic devices are described in U.S. Pat. Nos. 5,762,711; 5,877,093; 6,110,537; 6,287,985; and 6,319,740 to Heffner et al., the entire disclosures of which are incorporated by reference herein for all purposes.
Well-known thermal spraying processes can be used to provide high quality functional coatings on surfaces of electronic devices without damaging such devices. However, such thermal spraying processes have some shortcomings in some applications. Thermal spraying processes for certain electronic devices typically deposit such coatings at a deposition efficiency level less than about thirty percent. One reason for this is that many electronic devices are sensitive to heat and deposition efficiency decreases with deposition temperature. Thus, the deposition temperature for a thermal spraying process cannot be so high as to damage the electronic device being coated and deposition efficiency suffers from lower deposition temperatures. Moreover, the density of the coating is also related to deposition temperature. Specifically, coating density decreases with decreasing temperature. Yet, many coatings for electronic devices, such as those that are desired to be radio-opaque, would have improved shielding properties with higher density but practical restrictions on deposition temperature limit the density by which shield coatings can be formed on devices using thermal spraying.